C#5.0 采用CancellationTokenSource方式取消Task

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本文通过C#示例代码展示了如何使用CancellationTokenSource来取消正在运行的任务。文章首先创建了一个可取消的任务，并在任务开始执行前取消它。接着，演示了在任务运行过程中通过检查取消令牌来响应取消请求的过程。

贴一种取消任务的方式

using System;
using System.Threading;
using System.Threading.Tasks;

namespace CancellationDemo
{
    class Program
    {
        static void Main(string[] args)
        {
            var cts = new CancellationTokenSource();
            var longTask = new Task<int>(() => TaskMethod("task 1", 10, cts.Token), cts.Token);

            Console.WriteLine(longTask.Status);
            cts.Cancel();
            Console.WriteLine(longTask.Status);
            Console.WriteLine("first task has been cancelled before execution");

            //任务被取消后再运行为非法
            //longTask.Start();
            //Console.WriteLine(longTask.Status);
            //Console.WriteLine("----------------");

            cts = new CancellationTokenSource();
            longTask = new Task<int>(() => TaskMethod("task 2", 10, cts.Token), cts.Token);
            longTask.Start();
            for(int i = 0; i < 5; i ++)
            {
                Thread.Sleep(TimeSpan.FromSeconds(0.5));
                //Thread.Sleep(TimeSpan.FromSeconds(3.5));
                Console.WriteLine(longTask.Status);
            }
            Console.WriteLine("-----------------------");
            cts.Cancel();
            for (int i = 0; i < 5; i++)
            {
                Thread.Sleep(TimeSpan.FromSeconds(0.5));
                Console.WriteLine(longTask.Status);
            }
            Console.WriteLine("a task has been completed with result {0}.", longTask.Result);

            Console.ReadKey();
        }

        private static int TaskMethod(string name, int seconds, CancellationToken token)
        {
            Console.WriteLine("task {0} is running on a thread id {1}. Is thread pool thread: {2}",
                name, Thread.CurrentThread.ManagedThreadId, Thread.CurrentThread.IsThreadPoolThread);

            for(int i = 0;i < seconds; i ++)
            {
                Thread.Sleep(TimeSpan.FromSeconds(1));
                if (token.IsCancellationRequested)
                    return -1;
            }
            return 42 * seconds;
        }
    }
}